The present world economic growth points the considerable increase in demand for polyolefins, thus requiring an increase in the production of basic petrochemical products, chiefly ethene and propene.
The propene market is commanded by the strong demand for polypropylene, obtained through polymerization of propene gas (which is the monomer), using specific metallic catalysts. Ever since the introduction of polypropylene, it has become one of the most important thermoplastic resins, still being today the resin which sales grow the most in the world. At present, polypropylene is the third most sold thermoplastic in the world, representing physical sales of about US$17 million t/y with a value higher than US$11 billion/year.
In Brazil, Asia, Europe and Latin America, the predominant raw material for producing propene is naphtha. Over the last few years, refineries have increased much the volume of processed petroleum, and the naphtha market, for example, has been representing a crowing demand.
In this scenario, the need arises for considerably increasing the perspectives of investments in petrochemical plants, in technologies used by refineries and mainly in alternative sources of raw materials.
At present, the two traditional processes of producing ethane and propene are steam cracking and fluid catalytic cracking (FCC). Steam cracking of hydrocarbons is the main way of producing light olefins, especially ethane. The feed charges for the steam cracking units are mainly petrochemical naphtha, gasoils and condensates. On the other hand, with regard to FCC (fluid catalytic cracking), one can say that this is a process widespread in the world, due mainly to two factors. The first one is the fact of effectively contributing with the refinery to adjust the production thereof to the real needs of the local consumer market, in view of its great operational flexibility. The second factor that has made this a well-established process is related to the economic aspect, because FCC transforms residual fractions of low commercial value into noble derivatives of high value such as gasoline, liquefied petroleum gas (LPG) and basic petrochemicals like ethene and propene. The process consists in breaking heavy molecules present in gasoil and residues by the action of an amino-silicate based catalyst under high temperatures. The rupture of the bonds enables the production of light molecules, mainly compounds having from 3 to 12 carbon atoms (propene, LPG and gasoline), due to the selectivity of the catalyst used.
One of the emerging technologies for the production of olefins comprises Petrochemical FCC processes. They are substitutes for the conventional FCC process, but with much higher reaction temperature and catalyst circulation. This couple of values, which configures a high and severe condition, leads to the cracking of heavy and middleweight fractions, producing light compounds in the range of liquefied petroleum gas (LPG) and fuel gas. This, associated with the use of low pressure and adequate catalysts, maximizes the yield of light olefins. The operational conditions of Petrochemical FFC are much more severe than those of a conventional FFC process. As from a reaction temperature of 550° C. there is a substantial increase in the production of gas and LPG due to the cracking of gasoline. At approximately 600° C., the cracking of the LPG formed also takes place, and there is an exponential increase in the production of ethene. Therefore, the maximization of propene production requires reaction temperatures between 560° C. and 590° C., whereas the maximization of ethene requires even higher reaction temperatures, higher than 600° C.
Another emerging technology, still little employed, is the so called Methanol-to-Olefins (MTO) process, which is a technology of converting natural gas to olefins, known as Gas-to-Olefins (GTO) and which is based on a process of converting methanol to olefins, mainly ethene and propene, but butene as well. Natural gas is chiefly converted into methanol through the production of synthesis gas and subsequent reaction on suitable catalysts. The natural gas is firstly converted into methanol through the production of synthesis gas and further reaction onto appropriate catalysts. In the MTO process methanol is converted in a controlled way, under the action of a porous synthetic molecular sieve composed by silicon, aluminum and phosphorus oxides. These materials are combined with other components of the catalyst for selectively converting methanol to light olefins. Thus, the GTO process is a combination of the production of synthesis gas, production of methanol and conversion of methanol into olefins. The MTO process exhibits a global efficiency of 80%, based on the methanol used and enables a production of ethene and propene in ratios raging from 0.75:1 to 1.5:1 depending on the reactor conditions. The methanol production from synthesis gas is exothermic and favored under high pressures. The standard operation condition (for synthesis under low pressure) is 50 to 80 bar and temperatures ranging from 210 to 290° C. (input/output reactor). For up to 7% by mol of methanol at the reactor output, from 3.5 to 7% are recycled to the composition to achieve 90% to 97% of carbon monoxide conversion, which depends on the quality and composition of the gas, as well as on the recyclate ratio. The three main suppliers of the MTO process are UOP/Hydro, Lurgi and Exxon Mobil, with some variations among them. For instance, the Lurgi process produces only one olefin from methanol, namely propene, thus being called methanol-to-propylene (MTP).
Although the Methanol-to-olefin process is well known, is not yet employed on a large scale. Besides, the chemical reactions that take place are still not well understood and are the object of studies until today. At present, there are two demonstration plants for the MTO process in Norway, owned by Lurgi/Statoil and UOP Hydro. Although the MTO reactions are quite selective, by-products C4+ (butenes) are certainly also produced.
Another emerging technology for the production of propene is called “methatesis”. Olefin methatesis was observed for the first time in 1956 by the Petrochemistry Department of DuPont. The passage of propene through a molybdenum-aluminum catalyst provided a mixture of gases composed by ethylene and 1-butene. A similar result was achieved by researchers of Standard Oil Co., in 1960. In 1964, researchers of Phillips Petroleum Company were seeking the production of high-octane-number gasoline. Their intention was to produce iso-octane through the reaction between iso-butane and 2-butene, catalyzed by hexacarbonylmolybdenum supported on alumina. However, that reaction provided 2-pentene and propene, and said reaction was named “olefin deproportionation. In 1967, after a systematic study with unsaturated compounds researchers of Goodyear tire and Rubber Company suggested the name olefin methatesis for the newly discovered reaction. In the chemical sense, the word “methatesis” describes, by translation from the Greek language, “change of position”, that is to say, the change of covalent bonds between two alkenes (or olefins) or between an alkene and an alkyne. In the olefin chemistry, “methatesis” refers to a redistribution of the carbon backbone, on which carbon-carbon double bonds are rearranged in the presence of a metal-carbon complex, representing a catalytic method of breaking and forming multiple carbon-carbon bonds. This reaction is known in petrochemistry and in polymer chemistry since over 40 years ago, but only in the Nineties, with the advent of new and efficient catalysts developed mainly by the research groups of Schrock and Grubbs, it emerged as a powerful tool in the academic organic chemistry.
Finally, the technology referring to the Methanol-to-propylene (MTP) method, already cited before, corresponds to the transformation of methanol into propene (MTP). The Lurgi technology of transforming methanol to propene (MTP) is based on the efficient combination of two main characteristics:                1—fixed-bed reactor system, selected as the most suitable from the technological and economical point of view;        2—high selectivity and stability of the catalyst based on commercially manufactured zeolite.        
Methanol is catalytically converted into hydrocarbons, predominantly propene, and there is no production of ethene. Gasoline, LPG, fuel gas and water are by-products. At the MTP plant methanol is firstly converted to dimethylether (DME) and water, in a pre-reactor. By using a highly active and selective catalyst the thermodynamic balance is achieved, which results in a methanol/water/DME mixture under appropriate operational conditions. The conversion of methanol to DME exceeds 99%, with propene being the essential compound. Additional reaction procedures in the downstream reactor, in similar reaction conditions, provide maximum yield of propene. The product mixture that leaves the reaction system is at a low temperature. This consists of gaseous product, organic liquid and water, which need to be separated.
After compression of the gaseous product, traces of water, CO2 and DME are removed and the gas is processed with typical purity of over 97%. Various olefins are recycled to increase the yield of propene. In order to avoid the accumulation of inert materials in the recycle, a minor purge is required for light olefins and for C4/C5 cuts. Additional water resulting from the conversions of methanol is also removed. This water may be processed into drinking water.
The use of any of the raw materials mentioned so far to obtain propene will require new units to be designed (or the present ones to be adapted) for processing same. However, one can notice the need for investments in alternative sources of raw materials and for implantation of emerging technologies, so as to aggregate value to the petrochemical industry, thus meeting the demand for ethene and propene.
An alternative source for obtaining propene can originate from the main co-product of the production of biodiesel: glycerin. Biodiesel is composed of methyl or ethyl esters of fatty acids, and used in mixture with petrodiesel. Compared with diesel oil derived from petroleum, biodiesel can reduce up to 78% of carbon dioxide emissions, considering re-absorption by plants. Besides, it reduces by 90% the emissions of smoke and virtually eliminates sulfur oxide emissions. In general, this product is obtained from transesterification of plant oils with alcohols such as methanol and ethanol, using basic or acidic catalysis, or even by esterification of fatty acids in the presence of acidic catalysts.
From the chemical point of view, the production of biodiesel from plant oils involves a transesterification reaction. The plant oil is a triglyceride, that is, it is a tri-ester derived from glycerin or glycerol. Under the action of a basic or even acidic catalyst, and in the presence of methanol or ethanol, the oil undergoes a transesterification, forming three molecules of methyl or ethyl esters of fatty acids that compose plant oil, and releasing glycerin or glycerol, according to the scheme I:

For each 90 m3 of biodiesel produced by transesterification of plant oils, approximately 10 m3 of glycerin are formed. This scenario indicates that the commercial feasibility of biodiesel passes through the consumption of this extra glycerin volume, seeking large-scale applications, aggregating value to the production chain. Today, the main application of glycerin is in the cosmetic, soap and pharmaceutical industries, sectors that are incapable of absorbing, alone, the volume of glycerin generated with the production of biodiesel.
Thus, the risk of glycerin becoming an environmental problem, since there is no adequate demand for a growing volume of production of this product, can be considerably reduced. Besides, the fact that glycerin becomes a residue without commercial value checkmates the social-economical-environmental feasibility of biodiesel, at a time when the demand for it is increasing day by day due to the perception that biodisel is a cleaner source of energy, which generates social benefits as well.
Glycerol or glycerin is a triol with three carbon atoms. It has high viscosity and boiling point, being miscible with polar substances like water and immiscible with hydrocarbons and other non-polar compounds.
The hydrogenation of glycerin is described in the literature and leads to the obtainment of various substances, such as propyleneglycol, 1,2-propanodiol and 1,3-propanodiol, acetol, etc. However, the prior art does not present any process or reaction using homogeneous or heterogeneous catalysts in the presence of molecular hydrogen (H2) and that could make the production of propylene feasible.
The scientific literature reports a few examples of hydrogenation and hydrogenolysis of glycerin using various homogeneous and heterogeneous catalysts.
Runberg et al, Appl. Catal. 17, (1985) 309; Wojcik and Adkins, J. Am. Chem. Soc. 55, (1933) 1294; Wang et al. Ind. Eng. Chem. Res. 34, (1995) 3766-3770 and Lahr and Shanks, Ind. Eng. Chem. Res. 42, (2003) 5467-5472, describe, in recent studies, that conventional catalysts for hydrogenation of alcohols, such as nickel, ruthenium and palladium, are not effective for hydrogenation of glycerin. On the other hand, copper-based catalysts exhibit good results in hydrogenation of alcohols in general. These catalysts exhibit good selectivity for cleavage of the C—O bond and low affinity for C—C bonds. It should be pointed out that all these studies involve discontinuous reactor conditions.
Chaminand et al. Green Chem., 6, (2004) 359-361 describe the hydrogenation of an aqueous glycerin solution at 180° C. under an atmosphere of 80 bar of H2 and in the presence of Cu, Pd or Ru catalysts supported on ZnO, activated coal (C) or Al2O3. The reactions produce 1,2-propanodiol (1,2-PDO) and 1,-3-propanodiol (1,3-PDO) with good selectivity. Another important detail is the influence of the solvent (water, sulfonane, dioxane). The selectivity of 1,2-PDO increased significantly in the presence of the CuO/ZnO combination using water as a solvent. For a good selectivity to 1,3-PDO, the studies with Rh/C catalysts and sulfolane as a solvent presented good results. The addition of an additive (H2W04) has helped in improving the selectivity.
Dasari et al. Appl. Catal. A: Gen. 281, (2005), 225-231 describe the hydrogenation of glycerin into propylene glycol using nickel, palladium, platinum, copper and copper/chromium catalysts. At temperatures higher than 200° C. and under pressures of hydrogen of 200 psi, the propylene glycol selectivity decreases due to the excessive hydrogenolysis.
Xie end Schlaf, J. Mol. Catal. A: Chem. 229, (2005) 151-158 demonstrated that the hydrogenolysis of glycerin to 1,2-propanodiol and 1,3-propanodiol, using [cis-Ru(6,6-Cl2-biby)2(OH2)2](CF3SO3)2 as the catalyst in continuous stream of H2 under room pressure, besides being ecologically and economically feasible, does not generate the by-products derived from the polymerization and decomposition of triol, in drastic reaction conditions.
Hirai et al Energy & Fuels. 19, (2005) 1761-1762, describe a study in which ruthenium is dispersed in different carriers, such as: Y2O3, ZrO2, GeO2, La2O3, SiO2, MgO and Al2O3. These catalysts transformed glycerol into H2, CH4, CO and CO2. The catalyst that exhibited the best performance was Ru/Y2O3. The catalyst is pre-treated at 600° C. under a stream of H2 for 1 h. After this procedure, a stream of argon is used as carrier gas. With the aid of an injecting pump, an aqueous glycerin solution is slowly dropped onto the catalyst surface, which is at a temperature of 500° C. The generated gases are carried and analyzed in a gas chromatograph. With the 100% conversion to glycerin, the selectivity of the products varies between 60 and 80% for CO2 and between 80 and 90% for H2.
Chiu et al. Ind. Eng. Chem. Res. 45. (2006) 791-795 published a study according to which, after the transesterification process, calcium hydroxide in combination with phosphoric acid generates a precipitate characterized as hydroxyl-apatite, at different measurements of pH. Thus, raw glycerin can be used directly in the hydrogenolysis reaction for generating propylene glycol, without the yield being affected.
Recently, Miyazawa et al. Appl Catal. A: Gen. 318, (2007) 244-251, described the hydrogenation of glycerin to produce propylene glycol. The use of mild reaction conditions is still a great challenge for researchers, mainly at the hydrogenation step wherein usually lower temperatures work against the process. The Ru/C catalyst in combination with Amberlyst (ionexchange resin supplied by Rohm and Haas) exhibited good results. This catalyst was prepared from Ru(NO)(NO3)3 and activated charcoal, followed by a programmed-temperature procedure, under continuous air stream, which enabled a large surface area, which in combination with the acidity of Amberlyst, makes the reaction process much more efficient.
Maris and Davis, J. Catl. 249 (2007) 328-337 described the hydrogenation of glycerin on Ruthenium and Platinum catalysts supported on coal. The reaction was carried out with an aqueous glycerin solution at a temperature of 100° C. and under a pressure of 40 bar of hydrogen, leading to the production of ethylene glycol and propylene glycol.
The prior art also contemplates some patent documents relating to the glycerin hydrogenation and hydrogenolysis process.
The Chinese document CN 101085719 of Jun. 29, 2007, filed by Shanhai Huayi Acrylic Acid Co., describes a glycerin hydrogenation process in the temperature range of 180-300° C. and pressure from 1.0-10.0 MPa. The glycerin/H2 molar ratio is of 1:30 an the space velocity used was of 1.0-5.0 h−1 in the presence of Cu, Co and Al metallic oxides with percentage of 25% by weight of metal.
The Chinese document CN 101054339 of May 31, 2007, filed by Shanghai Huayi Acrilic Acid Co., describes another glycerin hydrogenation method using a mixture of gases and hydrogen in the presence of supported catalysts. The active component contains one or more metals, such as Ni, Co, Mn, Cu, Cr, Ca, Zn, Fe, Sn, W, Mo, V, Ti, Zr, Nb, La, Re, Ru, Rh, Pd and Pt. The temperature used ranges from 120 to 450° C., and the pressure ranges from 0.2 to 30.0 Mpa. The space velocity employed ranges from 0.1 to 50.0 h−1, and the glycerin/H2 molar ratio was of 1:(1-50). The support used comprises one or more of the following materials: zeolites, Al2O3, SiO2, MgO, TiO2, ZrO2, and amorphous aluminosilicates. The resulting products contain from 3 to 100% by weight n-propanol and one or more from methane, methanol, ethanol, ethylene glycol, 1,2-propanodiaol, 1,3-propanodiol, acetone and glycerin.
Chinese document CN101012149 of Feb. 7, 2007, filed by Univ. Nanjing, refers to a method of preparing 1,2-propanodiol under mild conditions, which comprises: using copper, zinc and manganese and/or aluminum as the catalyst; aerate glycerin and hydrogen continuously from the reactor top; hydrogenating glycerin at 200-250° C. under pressure of 2.5-5 MPa; extracting and collecting the reaction product from the catalyst bottom in a continuous manner; separating the gas; returning the gas to the recycle; and adjusting the weight rate of the metallic element of the catalyst.
Japanese document JP 2008044874 of Aug. 14, 2006, filed by Nat. Inst. Of Adv. Ind. & Technol., and Sakamoto Yakuhin Koogyo Co., Ltd., relates to a method of producing propanodiols, particularly 1,3-propanodiol, with a high yield by the glycerin hydrocracking method. Said method comprises hydrogenating glycerin in the presence of an acid and a hydrogenation catalyst, wherein a solvent may be also present in the reaction system, if circumstances so require. The acid is a solid at room temperature and the total weight ratio of the acid and of the hydrogenation catalyst to the total volume of glycerin and the solvent is of 1/15 to 10 g/mL.
Japanese document JP 416623,2 of Oct. 29, 1990, filed by Simitomo Metal Mining Co., refers to the obtainment of a catalyst for hydrogenation with high activity by depositing metals of the group VI (preferably Mo and/or W) and of the group VIII (preferably Co and/or Ni) on a catalytic support, with conversion of 99.4% and selectivity of 84.4 and 6%, respectively.
European document EP 0713849 of Nov. 17, 1995, filed by BASF AG, describes another glycerin hydrogenation process for the production of isopropanol, n-propanol and propanodiols, using metallic catalysts containing supported cobalt, copper, manganese or molybdenum and an inorganic polyacid. The yield obtained was 95%, the pressure was 3625 psi and the temperature of 250° C.
European document EP0598228 of Oct. 18, 1993, filed by Degussa A G, discloses a process of simultaneously producing propylene glycol and 1,3-propanodiol (1,3-PDO) by hydrogenation and hydrogenolysis of glycerin/water solutions containing 10-40-% by weight of glycerin at a temperature of 300° C.
German document DE 4302464 of Jan. 29, 1993, filed by Henkel KgaA, describes the process of glycerin hydrogenation to 1,2-propylene glycol in vapor phase with high conversion and selectivity. The temperature of the reaction ranges from 160 to 260° C., the pressure ranges from 10 to 30 bar and the glycerin/H2 molar ratio is of 1:600.
Analyzing the above-cited prior art, it can be observed that most of the documents presented relate to glycerin hydrogenolysis. However, the final product of interest is not propene. Many of the documents analyzed have, as a product of interest, chiefly ethylene glycol, 1,2-propanodiol and 1,3-propanodiol. By virtue of this result, it is concluded that the catalysts used in those cases would not be capable of acting in a propene-selective manner due to the fact that the operational conditions are different, such as space velocity, glycerin/hydrogen molar ratio, reaction time, among others. Therefore, the technique of using catalysts prepared according to the present invention for obtaining propene in a selective manner is not an obvious result from the prior art to a person skilled in the art.
As mentioned before, there is a growing need to absorb the glycerin charge produced as a by-product of the preparation of biodiesel. Moreover, the strong demand for propene, which is the precursor of polypropylene, and the search for technologies that are cleaner and less aggressive to the environment are decisive factors that prove the need for new techniques.